diff --git a/lib/http/rpc.js b/lib/http/rpc.js
index 3b6d51e1..7e2e3760 100644
--- a/lib/http/rpc.js
+++ b/lib/http/rpc.js
@@ -708,6 +708,9 @@ RPC.prototype.getRawMempool = co(function* getRawMempool(args, help) {
   if (help || args.length > 1)
     throw new RPCError('getrawmempool ( verbose )');
 
+  if (!this.mempool)
+    throw new RPCError('No mempool available.');
+
   if (verbose) {
     hashes = this.mempool.getSnapshot();
 
@@ -748,8 +751,11 @@ RPC.prototype.getTXOut = co(function* getTXOut(args, help) {
   if (!hash || index == null)
     throw new RPCError('Invalid outpoint.');
 
-  if (mempool)
+  if (mempool) {
+    if (!this.mempool)
+      throw new RPCError('No mempool available.');
     coin = this.mempool.getCoin(hash, index);
+  }
 
   if (!coin)
     coin = yield this.chain.db.getCoin(hash, index);
@@ -1352,7 +1358,7 @@ RPC.prototype.prioritiseTransaction = co(function* prioritiseTransaction(args, h
   var valid = new Validator([args]);
   var hash = valid.hash(0);
   var pri = valid.num(1);
-  var fee = valid.num(2);
+  var fee = valid.i64(2);
   var entry;
 
   if (help || args.length !== 3) {
@@ -1374,6 +1380,8 @@ RPC.prototype.prioritiseTransaction = co(function* prioritiseTransaction(args, h
   if (!entry)
     throw new RPCError('Transaction not in mempool.');
 
+  this.mempool.prioritise(entry, pri, fee);
+
   return true;
 });
 
@@ -1673,6 +1681,9 @@ RPC.prototype.signRawTransaction = co(function* signRawTransaction(args, help) {
   if (!data)
     throw new RPCError('Invalid hex string.');
 
+  if (!this.mempool)
+    throw new RPCError('No mempool available.');
+
   tx = MTX.fromRaw(data);
   tx.view = yield this.mempool.getSpentView(tx);
 
diff --git a/lib/mempool/mempool.js b/lib/mempool/mempool.js
index e69273a3..a117ec54 100644
--- a/lib/mempool/mempool.js
+++ b/lib/mempool/mempool.js
@@ -1953,6 +1953,29 @@ Mempool.prototype.getSize = function getSize() {
   return this.size;
 };
 
+/**
+ * Prioritise transaction.
+ * @param {MempoolEntry} entry
+ * @param {Number} pri
+ * @param {Amount} fee
+ */
+
+Mempool.prototype.prioritise = function _prioritise(entry, pri, fee) {
+  if (-fee > entry.deltaFee)
+    fee = -entry.deltaFee;
+
+  if (-pri < entry.priority)
+    pri = -entry.priority;
+
+  this.updateAncestors(entry, preprioritise);
+
+  entry.priority += pri;
+  entry.deltaFee += fee;
+  entry.descFee += fee;
+
+  this.updateAncestors(entry, prioritise);
+};
+
 /**
  * MempoolOptions
  * @alias module:mempool.MempoolOptions
@@ -2571,7 +2594,7 @@ function nop(parent, child) {
 }
 
 function addFee(parent, child) {
-  parent.descFee += child.fee;
+  parent.descFee += child.deltaFee;
   parent.descSize += child.size;
 }
 
@@ -2580,10 +2603,18 @@ function removeFee(parent, child) {
   parent.descSize -= child.descSize;
 }
 
+function preprioritise(parent, child) {
+  parent.descFee -= child.deltaFee;
+}
+
+function prioritise(parent, child) {
+  parent.descFee += child.deltaFee;
+}
+
 function cmpRate(a, b) {
-  var xf = a.fee;
+  var xf = a.deltaFee;
   var xs = a.size;
-  var yf = b.fee;
+  var yf = b.deltaFee;
   var ys = b.size;
   var x, y;
 
@@ -2609,7 +2640,7 @@ function cmpRate(a, b) {
 }
 
 function useDesc(a) {
-  var x = a.fee * a.descSize;
+  var x = a.deltaFee * a.descSize;
   var y = a.descFee * a.size;
   return y > x;
 }
diff --git a/lib/mempool/mempoolentry.js b/lib/mempool/mempoolentry.js
index 09ab312f..07cebbab 100644
--- a/lib/mempool/mempoolentry.js
+++ b/lib/mempool/mempoolentry.js
@@ -40,6 +40,7 @@ function MempoolEntry(options) {
   this.sigops = 0;
   this.priority = 0;
   this.fee = 0;
+  this.deltaFee = 0;
   this.ts = 0;
   this.value = 0;
   this.dependencies = false;
@@ -63,6 +64,7 @@ MempoolEntry.prototype.fromOptions = function fromOptions(options) {
   this.sigops = options.sigops;
   this.priority = options.priority;
   this.fee = options.fee;
+  this.deltaFee = options.deltaFee;
   this.ts = options.ts;
   this.value = options.value;
   this.dependencies = options.dependencies;
@@ -112,6 +114,7 @@ MempoolEntry.prototype.fromTX = function fromTX(tx, view, height) {
   this.sigops = sigops;
   this.priority = priority;
   this.fee = fee;
+  this.deltaFee = fee;
   this.ts = util.now();
   this.value = value;
   this.dependencies = dependencies;
@@ -160,9 +163,9 @@ MempoolEntry.prototype.txid = function txid() {
  */
 
 MempoolEntry.prototype.getPriority = function getPriority(height) {
-  var heightDelta = height - this.height;
-  var deltaPriority = (heightDelta * this.value) / this.size;
-  var result = this.priority + Math.floor(deltaPriority);
+  var height = height - this.height;
+  var priority = (height * this.value) / this.size;
+  var result = this.priority + Math.floor(priority);
   if (result < 0)
     result = 0;
   return result;
@@ -177,6 +180,15 @@ MempoolEntry.prototype.getFee = function getFee() {
   return this.fee;
 };
 
+/**
+ * Get delta fee.
+ * @returns {Amount}
+ */
+
+MempoolEntry.prototype.getDeltaFee = function getDeltaFee() {
+  return this.deltaFee;
+};
+
 /**
  * Calculate fee rate.
  * @returns {Rate}
@@ -186,6 +198,15 @@ MempoolEntry.prototype.getRate = function getRate() {
   return policy.getRate(this.size, this.fee);
 };
 
+/**
+ * Calculate delta fee rate.
+ * @returns {Rate}
+ */
+
+MempoolEntry.prototype.getDeltaRate = function getDeltaRate() {
+  return policy.getRate(this.size, this.deltaFee);
+};
+
 /**
  * Calculate fee cumulative descendant rate.
  * @returns {Rate}
@@ -322,6 +343,7 @@ MempoolEntry.prototype.fromRaw = function fromRaw(data) {
   this.sigops = br.readU32();
   this.priority = br.readDouble();
   this.fee = br.readU64();
+  this.deltaFee = this.fee;
   this.ts = br.readU32();
   this.value = br.readU64();
   this.dependencies = br.readU8() === 1;
diff --git a/lib/mining/template.js b/lib/mining/template.js
index f635ed80..b259a969 100644
--- a/lib/mining/template.js
+++ b/lib/mining/template.js
@@ -649,9 +649,9 @@ BlockEntry.fromTX = function fromTX(tx, view, attempt) {
 BlockEntry.fromEntry = function fromEntry(entry, attempt) {
   var item = new BlockEntry(entry.tx);
   item.fee = entry.getFee();
-  item.rate = entry.getRate();
+  item.rate = entry.getDeltaRate();
   item.priority = entry.getPriority(attempt.height);
-  item.free = item.fee < policy.getMinFee(entry.size);
+  item.free = entry.getDeltaFee() < policy.getMinFee(entry.size);
   item.sigops = entry.sigops;
   item.descRate = entry.getDescRate();
   return item;
diff --git a/lib/utils/validator.js b/lib/utils/validator.js
index 147e4a69..3f4dceff 100644
--- a/lib/utils/validator.js
+++ b/lib/utils/validator.js
@@ -197,6 +197,50 @@ Validator.prototype.u64 = function u64(key, fallback) {
   return value;
 };
 
+/**
+ * Get a value (as an int32).
+ * @param {String} key
+ * @param {Object?} fallback
+ * @returns {Number|null}
+ */
+
+Validator.prototype.i32 = function i32(key, fallback) {
+  var value = this.num(key);
+
+  if (fallback === undefined)
+    fallback = null;
+
+  if (value === null)
+    return fallback;
+
+  if (value % 1 !== 0 || Math.abs(value) > 0x7fffffff)
+    throw new Error(fmt(key) + ' must be an int32.');
+
+  return value;
+};
+
+/**
+ * Get a value (as an int64).
+ * @param {String} key
+ * @param {Object?} fallback
+ * @returns {Number|null}
+ */
+
+Validator.prototype.i64 = function i64(key, fallback) {
+  var value = this.num(key);
+
+  if (fallback === undefined)
+    fallback = null;
+
+  if (value === null)
+    return fallback;
+
+  if (value % 1 !== 0 || Math.abs(value) > 0x1fffffffffffff)
+    throw new Error(fmt(key) + ' must be an int64.');
+
+  return value;
+};
+
 /**
  * Get a value (as a satoshi number or btc string).
  * @param {String} key